Ubuntu 22.04 LTS DNS Resolution Intermittently Fails with systemd-resolved

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Hosts intermittently fail DNS lookups, causing apt, API calls, and service discovery to break unpredictably. Applications appear unstable despite healthy network connectivity.

Environment & Reproduction

Ubuntu 22.04 LTS uses systemd-resolved with stub resolver at 127.0.0.53. Reproduce under upstream DNS latency, inconsistent DHCP-provided servers, or split-DNS misconfiguration.

Root Cause Analysis

Failures often come from unreachable upstream nameservers, invalid search domains, or resolver cache states combined with network transitions across interfaces and VPN links.

Quick Triage

Test direct DNS queries against configured upstreams and inspect current resolver status before restarting services. This distinguishes resolver service issues from external DNS outages.

Step-by-Step Diagnosis

Review resolved logs, interface DNS assignments, and query latency. Confirm whether failures are domain-specific, link-specific, or global across all nameservers.

Solution – Primary Fix

Set reliable DNS servers in netplan, apply configuration, and restart resolved service. Clear stale cache and verify deterministic query responses across repeated tests.

Solution – Alternative Approaches

Use local caching resolver like Unbound, set per-link DNS for VPN domains, or disable problematic DHCP DNS propagation where static resolver policy is required.

Verification & Acceptance Criteria

Repeated DNS queries return quickly without timeout, application endpoints resolve consistently, and resolver logs remain free of upstream failure bursts.

Rollback Plan

Restore prior netplan file, reapply networking, and restart systemd-resolved. If needed, temporarily point to known public resolvers while root-cause review continues.

Prevention & Hardening

Monitor DNS latency/error rates, define primary/secondary resolvers explicitly, and validate split-horizon DNS behavior in staging for all critical domains.

Related Errors & Cross-Refs

Often adjacent to DHCP lease churn, VPN route precedence issues, and stale /etc/resolv.conf symlink states in manually modified systems.

Related tutorial: View the step-by-step tutorial for Ubuntu 22.04 LTS.

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Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

Consult systemd-resolved documentation, netplan docs, and man pages for resolvectl(1), resolved.conf(5), and dig(1).